Holding device for flexographic printing sleeves

ABSTRACT

The invention relates to a holding device for a flexographic printing sleeve, which comprises at least one receiving member exhibiting a cylindrical side surface over which a printing sleeve can slide, said receiving member being able to rotate around its longitudinal axis and around the sleeve longitudinal axis. According to the invention, the receiving member comprises two or more shoulders with differing diameters and the holding device comprises a second identical receiving member. Both receiving members are placed in such a way that they can rotate around the same longitudinal axis and are oriented toward each other with their small shoulders. At least one of the receiving members can be moved along said longitudinal axis in such a way that the distance between said two receiving members can be adjusted.

BACKGROUND OF THE INVENTION

The invention relates to a holding device for a flexographic printingsleeve.

A nongeneric holding device for a printing cylinder is already knownfrom FR 1275904. This device has two conical receiving members for theprinting cylinder provided with the printing image.

The fundamentally narrow contact surface between cone and cylinderproviding the purely frictional transmission of force from therotationally driven conical receiving members to the printing cylinderis disadvantageous in that comparatively heavy, thick-walled printingcylinders must be used which provide a sufficiently large contactsurface for transmission of force through beveling at the two end facesof the cylinder. This large wall thickness also ensures that thecompressive forces needed to hold the printing cylinder in place betweenthe two receiving members do not deform the printing cylinder.

CH 377854 also discloses a likewise non-generic clamping device for thebearing support of rollers with paper, foil, and the like, in whichdevice each end of the roller attaches to a conical receiving member inthe form of a clamping cone. A form-fitting element acting as arotational locking element is provided between the sleeve-shaped rollercore and the clamping cone.

For this purpose, either a plurality of ribs and matching grooves mustbe formed on these two components, or the clamping cone must be moldedin the material of the roller core such that this roller core ispermanently deformed.

The device presented in CH 377854 is designed for holding onlysingle-use rollers.

When the design disclosed in CH 377854 is transferred to printingequipment, the addition of grooves or ribs in sleeves of small wallthickness would not be possible. Permanent deformation of the printingsleeves by the receiving members would inhibit or preclude the multipleuse of the printing sleeves, and would also carry the additional riskthat the surface with the printing image would exhibit undesirableeccentricities.

In contrast to the teaching of FR 1275904, in one type of printingtechnology called “flexographic printing” instead of a completeone-piece printing cylinder, each with its own printing image,replaceable sleeves are used which may be slipped onto a cylindricalmetal receiving member.

DE 2700118C2 or DE 3633155A1 disclose generic holding devices in whichthe cylindrical metal receiving member in each case extends through theentire length of the sleeve. The cylindrical receiving member is inother words a “permanent printing cylinder” since it may be used withmultiple sleeves and thus for multiple printing images. Here each sleevecan display the printing image directly, for example etched or burned inby laser, or it can have a separate external plate layer with theprinting image.

To mount the sleeves in flexographic equipment, compressed air exits theinner cylindrical receiving member and expands the partially mountedsleeve so that this may be slipped completely onto the receiving member.When the compressed air is switched off, the sleeve constricts and liesfirmly in place on the cylindrical receiving member such that the sleevemay rotate together with the latter. The cylindrical receiving member ismade of metal, and its resulting high cost of production and high weightimpeding handling are thus disadvantageous.

In addition to utilization in the printing facilities themselves, i.e.in the printing presses, many of these devices are employed in theprocessing stations which are needed to create a printing sleeve andwhich also have a rotatable holder for the printing sleeves or theirassociated preliminary production stages, for example coating machineswhich coat the surface of the unfinished sleeve with light-sensitive oracid-sensitive materials by which the printing images are later appliedto the sleeve surface by laser-based or etching processes. These etchingor laser machines also require this type of rotatable holder for theprinting sleeves.

Both during printing as well as during the preparatory productionprocesses for the printing sleeves, a fundamental problem consists inthe fact that printing sleeves of widely varying outside diameters arerequired. In one comparatively old technology, noticeably thin-walledmetal printing sleeves were slipped onto cylindrical receiving members.The wall thickness of these sleeves had to be small to ensure theflexibility needed to allow the sleeves to be expanded by compressedair. As result, the cylindrical receiving members had almost the samediameters as the printing sleeves. Given a variety of outside sleevediameters for the varying sizes of the printing images, a matchingnumber of receiving members of varying diameters had to be kept on hand.

One simplification of the above for the user lies in the fact thatsleeves of varying wall thickness may be used with receiving members ofthe same diameter so that a greater number of sleeves of varying outsidediameters may be used where a reduced number of different receivingmembers are employed. Based in part on the use of plastics, thesesleeves exhibit the flexibility needed to be expanded by compressed airdespite these wall thicknesses.

Nevertheless, it is common to have a gradation in 10 mm steps of theoutside diameters of the cylindrical receiving members. Given a sizerange of around 250 mm to 2000 mm for the sleeve circumferences matchingthe size of the printing images, even in the flexographic process acomparatively large number of receiving members need be kept on hand.This requires a very high total investment for the printing facilities,especially for the above-mentioned shops involved in the preparatoryproduction: whereas a printing facility may specialize in processingprinting images within a limited size range, laser-gravure and similarfacilities are usually oriented around creating sleeves for the entirerange of the above sleeve circumferences.

As a result, to reduce in practice the inventory of receiving memberswith differing outside diameters, sleeves are employed having sometimesvery large wall thicknesses so that a sleeve of large outside diameterwith a correspondingly large printing image may be used on a “small”receiving member.

The result is considerable expense and effort, especially when sleevesof such large wall thickness or diameter are used due to theconsiderable weight of such sleeves and especially of their associatedcylindrical receiving members. Not all facilities have suitable in-planthandling equipment such as cranes, lifts, or the like which require avery high investment. For this reason, only sleeves of comparably smalldiameter can be processed. In addition, set-up times for changingreceiving members are considerably shorter and thus more inexpensive ifthis change can be effected by hand, i.e. without such handlingequipment.

SUMMARY OF THE INVENTION

The object of the invention is to improve a generic holding device suchthat the most inexpensive possible holding device simplifies thefollowing: handling of the receiving member when the receiving member ischanged, sleeve changeovers, and the changeovers of sleeves withdifferent diameters.

This object of the invention is achieved by a holding device for aflexographic printing sleeve according to the teachings of the presentinvention.

The invention proposes, in other words, using two receiving membersinstead of one, which receiving members receive the sleeve between them,the receiving members each having two or more shoulders with varyingdiameters.

In contrast to a single cylindrical receiving member which extends theentire length of the printing sleeve, as is well known in flexography,the invention provides for considerable savings in weight, therebysimplifying handling when the receiving member or holding device ischanged. Specifically, such changes are required less often since thereceiving members allow various sleeves of differing inside diameters tobe handled.

In contrast to the utilization of two conical receiving members familiarfrom other technical areas, axial compressive forces are avoided here sothat even very thin-walled sleeves may be retained securely and withoutdeformation. In addition, reliable support is provided in particular forextremely thin-walled sleeves by the cylindrical lateral surfaces:thin-walled sleeves which are often out of round at first are securelycentered, after mounting on the receiving member, by the circular,constant-diameter circumference of the shoulder and take on a completelycircular outer contour—thereby facilitating processability of anunfinished sleeve or ensuring a precise and uniform print image in thecase of a finished printing sleeve.

In this way, sleeves of highly varying outside diameters may be held inplace on the same receiving member while the wall thickness of thesleeves can remain comparatively small since the sleeve may be slippedonto the section of the receiving member which most nearly approximatesthe desired outside diameter of the sleeve. Three advantages result fromthis:

1. Handling of the receiving members during its exchange is simplifiedbecause two rather than one receiving member are provided, eachindividual receiving member thus being of lighter weight, and becausethe two receiving members together do not extend over the entire lengthof the sleeve; instead each receiving member is located only in theregion of one end of the sleeve.

2. Exchange of the sleeves is simplified because the use of shoulders inthe receiving members allows the wall thickness of the sleeve tooptimally approximate the desired outside diameter—with the result thatthin-walled, and thus correspondingly light-weight sleeves may beprovided which are therefore easy to handle.

3. Exchange of the sleeves with differing diameters is in many casessimplified because the receiving members often do not have to bereplaced. Instead, in many cases simply another shoulder of thereceiving member may be used for the new sleeve which has a insidediameter different from that of the previously used sleeve.

To change the sleeves, both receiving members may be “opened” in thefamiliar fashion, i.e. moved apart, while to secure the sleeves the tworeceiving members are then moved back together. A system may be providedhere whereby the two receiving members are arranged on a common,physically realized axis on which at least one of the receiving membersis mounted so as to be longitudinally movable. In an alternative system,the two receiving members are arranged on a virtual common rotational orlongitudinal axis, for example by having both receiving membersrotationally mounted and freely protruding, each at one base.

The two-piece design of the previously one-piece, cylindrical, metalreceiving member, as well as the gradation into smaller diameters and adesign length which may be shorter than half of a previous,traditionally used receiving member, all combine to result in aconsiderable reduction in the weight of the individual manipulatedcomponents such that as a rule the use of a crane is not required.

As a result of the reduced weight, the bearings of the receiving memberin the holding device may be designed to be smaller and cheaper. Fewerreceiving members must be kept on hand since sleeves of different insidediameters may be used on the same receiving member. An additional factoris the elimination of handling equipment such as cranes or the like.

A fourth advantage is the fact that production costs for the holdingdevice are lower, and specifically that overall investment costs for theuser are considerably reduced as compared with those incurred by the useof traditional holding devices.

Set-up times are considerably reduced since sleeves of differentdiameters may be used on the same receiving member and replacement ofthe receiving member is seldom required. It is not only the mountingtime which must be considered here but also the subsequent inspection toverify the concentricity and cylindricity of the receiving member.Operating costs are also lower than when traditional receiving membersare used.

Since the receiving members do not support the sleeve along its entirelength, the risk of the sleeve sliding out of position when thereceiving member is driven can be avoided by providing teeth between thereceiving member and the sleeve, the teeth being in either an axialand/or radial orientation. To preclude the risk of deforming thin-walledsleeves, or if the wall thickness of the sleeve does not allow for theteeth, an alternative approach is to roughen the lateral surface of theshoulders to increase friction or to coat them - thereby enhancing thefrictional connection to the sleeves.

According to the invention, the receiving members take up a maximum ofhalf the length of the receiving tube if both receiving members areinexpensively designed to be the same. To ensure a secure grip of thesleeve, the section of the receiving member extending into the sleevemust not be shorter than a certain minimum length which depends, forexample, on the materials used and on the possible teeth or frictionalproperties given to the surface. As a result, the number of shouldersfor each receiving member is limited.

In order to utilize the greatest possible range between 250 mm and 2,000mm of the sleeve circumference, multiple types of receiving members maybe provided for which the shoulder diameters vary from type to type.

In order to make replacement of the receiving members even moreinfrequent and to keep these receiving members available as often aspossible, an additional component may be provided in the holding devicewhich renders the sleeve quasi-two-layered, i.e., an inner “supportsleeve” onto which the actual sleeve to be processed or having the printsurface can be slipped in the familiar fashion for flexographicequipment. The support sleeve, in other words, represents theintermediate stages which the receiving member does not have due to theabove limitations.

The support sleeve may advantageously be rigid, lightweight, andnonflexible, consisting, for example, of a material such as foamaluminum or the like, of fiber composites, or of a sandwichconstruction, while the actual sleeve may consist of a more flexible(and possibly heavier) material which facilitates mounting typical inflexography. This mounting may be either on the support sleeve, forexample initially for processing the unfinished sleeve or also onprinting presses that have the staged receiving members as well as asupport sleeve. Mounting may, however, also be on printing presses whichhave traditional one-piece receiving members.

To enable the sleeve to be mounted, the support sleeve has air channelsallowing compressed air to be conveyed from an air compressor throughthe support sleeve and the outer sleeve to be slipped on in the fashiontypical of flexography. The “complete sleeve” consisting of the actualsleeve and the support sleeve may now be easily handled and held betweenthe receiving members.

The support sleeve, in other words, replaces the comparatively muchheavier and more expensive flexographic cylinder. Even when the sleevesare not immediately mounted on the receiving members and only additionalsupport sleeves are utilized, there are considerable advantages in termsof handling.

Due to the fact that multiple support sleeves of different outsidediameters may be designed, a precise gradation of the overall system ispossible in which the receiving members are designed with few shoulders,and fine adjustment to match nearly any outside diameter of the printingsleeves is effected by the use of the appropriate support sleeves. Inaddition, the support sleeve reinforces the sleeves of small wallthickness, thereby creating a stronger complete sleeve and facilitatingthe handling of the sleeves without damage. Specifically, this factorenables attachment to the receiving members in a way in whichnonreinforced sleeves could be damaged; for example when teeth areprovided and a very thin-walled sleeve is to be used, or when the sleevedoes not expand in the typical flexographic fashion to be released fromthe receiving member but is instead mechanically clamped to thereceiving member.

The use of support sleeves considerably simplifies and speeds up thehandling of the sleeves: Instead of lifting the traditional printingcylinder with a crane into a special mounting device from which it isslipped onto the sleeve, the support sleeve may be placed vertically onthe floor and attached by a quick-release device to the compressed-airsupply so that the sleeve may subsequently be “slipped over.” Also,instead of inserting the traditional printing cylinder with the sleeveinto the processing or printing press and setting concentricity andcylindricity, the “complete sleeves” consisting of sleeve and supportsleeve may be mechanically clamped between the receiving members withoutthe need for further alignment. Specifically, the time for sleevereplacement may be reduced to ⅕ or {fraction (1/10)} of the timetraditionally required.

To facilitate handling and enable the lowest weight possible for sleevesand support sleeves, the latter may have the smallest wall thicknessespossible. To preclude deformation and damage both during processing andalso later during the printing operation, the sleeves or support sleevesmay have reinforcing elements in their inner cavity, for example, a coremade of fiber composite materials or of a light-weight material such asfoam aluminum, or extruded sections, for example made of aluminum havinga cross-section which is, for example, stellate or cruciform or ofsimilar design, or for example in the shape of a polygonal tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the holding device of the presentinvention; and

FIG. 2 is a schematic view of a holding device of the present inventionhaving air channels.

DESCRIPTION OF ILLUSTRATED EMBODIMENT

A purely schematic cross section through a holding device 1 is shownwhich serves to hold sleeves 2, sleeves 2 acting as “printing sleeves,”this term referring to the use of sleeves 2 in the printing industry.Sleeve 2 may be ready for use, or it can also be an “unfinished” sleevewhich passes through certain production stages to create a ready-to-useprinting sleeve.

Each end face of sleeve 2 is slipped onto one receiving member 3 whichin turn has multiple shoulders 4 of different diameters with cylindricallateral surfaces. Shown simply as an example, some shoulders areprovided with four chamfers which facilitate the slipping on of thesleeves onto the receiving members 3; however the receiving members 3may also be designed without such chamfers or with chamfers on allshoulders 4.

Both receiving members 3 are rotatable. Here the receiving member 3shown at the left is held in the base indicated which represents anondriven support. At the receiving member 3 shown at the right is ashaft end which leads to a machine base which contains a drive unit forthis right-hand receiving member 3 such that the sleeve 2 may be causedto rotate. Deviating from this embodiment, both receiving members 3 maybe rotationally driven synchronously. The right-hand receiving member 3may be axially 9 displaced along with the shaft whose shaft end isindicated within a plain bearing of the machine base not shown, orpossibly displaced together with the machine base, so as to position thesleeves 2 between the receiving members 3, or to remove them from thereceiving members 3, as well as to adjust the distance between thereceiving members 3 to the differing lengths of sleeves 2. The axial 9displacement of the receiving member 3 may be effected, for example,pneumatically since the mounting of sleeves is typically effected inflexography by compressed air.

A rotationally locked retention of sleeve 2 on the receiving member 3 isensured by toothed elements 5 which extend into a support sleeve 6carrying the sleeve 2. The toothed elements 5 are shown in thisembodiment purely schematically, and as an example, asaxially-parallel-running pins which are provided on the receivingmembers 3. The complete sleeve composed of the actual sleeve 2 and thesupport sleeve 6 has in the support sleeve 6 matching toothed elementsto receive the pins. Deviating from this purely schematicrepresentation, the wall thicknesses of sleeve and support sleeve may bequite different. A thin-walled sleeve may, for example, be mounted on athick-walled support sleeve—with the greater wall thickness of thesupport sleeve permitting as needed the design of the toothed elementswhich possibly could not be realized within the sleeve due to its smallwall thickness.

The support sleeve 6 has air channels 10 through which compressed air isconducted to the lateral surface of the support sleeve 6 so that thesleeve 2 may be attached in the familiar fashion to the support sleeve 6to form the complete sleeve. Irrespective of the material used for thesupport sleeve 6, provision can be made to create the air channels outof pressure-resistant hoses or tubes, for example made of metal orplastic which may be arranged in the wall of the thick-walled supportsleeves 6, for example having been molded in, foamed in or laminated in,and which may be fixed along the interior side of thin-walled supportsleeves 6, for example screwed in and/or glued. Passage bores may beprovided to conduct the air from the air channels to the lateral surfaceof the support sleeve 6.

Mounting of the sleeve 2 onto the support sleeve 6 occurs in a set-upstation before the complete sleeve formed from sleeve 2 and supportsleeve 6 is secured in the device 1. Since the support sleeve 6 mayconsist of a lightweight composite, a foam metal, or the like, thelightweight design is achieved, and thus the simple, crane-less handlingof the above-mentioned complete sleeve as well.

The device 1 shown may be provided in the area of a processing stationin which a printing sleeve is produced from sleeve 2, in this casesleeve 2 being an unfinished sleeve. If needed, however, the printingunit itself may be equipped with such a device 1 in place of thetraditional printing cylinders to receive sleeve 2, in this case sleeve2 being a printing sleeve.

The support sleeve 6 serves as a kind of adapter to receive the actualsleeve 2 which has the printing image. Such adapters may be eliminatedif the receiving members 3 have shoulders 4 with suitable diameters forthe desired sleeves 2 and if the sleeve can be properly secured on thereceiving member 3, for example by suitable teeth (form-fittingconnection) or by the rigidity which a fixed rotationally lockedclamping (frictional connection) of the sleeve 2 between the receivingmembers 3 allows. This rigidity may be achieved with plastic sleeves,for example by fiber reinforcements. The frictional connection mayadditionally be improved by the friction-enhanced design of theinteracting surfaces of the sleeve and receiving member.

Thus, depending on the usual specification profile for the individualusers, different receiving members with differing shoulder diameters maybe provided. In addition, an alternative to using the support sleeve 6is that the user, in order to use the sleeves 2 with differing insidediameters, employs instead the comparatively small and light,easy-to-handle receiving members 3 of the device 1 so that the receivingmembers 3 may be used which have a shoulder 4 with the outside diameterappropriate for the inside diameter of the sleeve 2 or the supportsleeve 6 which are to be employed.

If no support sleeves are to be used, air channels 8 may be provided inthe receiving members 3 in a manner similar to that for the familiar,comparatively large cylinders known in the field of flexography: Herethe outlet openings for the air are provided in the lateral surfaces ofthe shoulders to expand the sleeves 2 and enable them to be slippeddirectly onto the receiving members 3. Outlet openings on shoulders notused may be blocked or closed by means of suitable valves or plugs.

What is claimed is:
 1. Holding device for a flexographic printingsleeve, the holding device having at least one receiving member with acylindrical lateral surface for mounting the printing sleeve, thereceiving member being rotatable about a longitudinal axis of theprinting sleeve, characterized in that the receiving member has two ormore shoulders of differing diameters and that a second, equivalentreceiving member is provided, both receiving members being arranged androtatable about the longitudinal axis, and the receiving members withtheir smallest shoulders being aligned with each other, and at least onereceiving member being adjustable along the longitudinal axis to set avariable distance between both receiving members, and an inner supportsleeve to receive the sleeve, the support sleeve having air channelsleading from an end face or from an inner surface of the support sleeveto an outer surface of the support sleeve.
 2. Device according to claim1, characterized in that the receiving member has toothed elements inradial or axial orientation which interface with corresponding toothedelements allocated to the sleeves.
 3. Device according to claim 1,characterized in that the sleeve has reinforcing elements in an cavity.4. Device according to claim 1, characterized in that the support sleevehas reinforcing elements in an inner cavity.